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Conterminous United States Remote Sensing Phenology Metrics Database

December 2, 2021

Phenological dynamics of terrestrial ecosystems reflect the response of the Earth's vegetation canopy to changes in climate and hydrology and are thus important to monitor operationally. Researchers at the U.S. Geological Survey (USGS), Earth Resources Observation and Science (EROS) Center have developed methods for documenting the seasonal dynamics of vegetation in an operational fashion from satellite time-series data. The phenological metrics data produced at USGS EROS provide indicators of key phenological events for the conterminous United States on a yearly basis from 1989 to present. As the objective is to monitor the phenological dynamics of the vegetation canopy across large areas rather than specific plants over limited space, the use of satellite imagery provides the basis to measure large scale change at the ecosystem level. Time series observations from the National Oceanic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR) and the National Aeronautics and Space Administration's (NASA) MODerate Resolution Imaging Spectroradiometer sensors provide the source data for this USGS phenological database. The complete set of phenological metrics are as follows:
1. Start of Season Time (SOST): starting time of the onset of the growing season (in day of the year). 2. Start of Season NDVI (SOSN): NDVI value at the starting time of the onset of the growing season (unitless- based on NDVI units). 3. End of Season Time (EOST): ending time of the growing season (in day of the year). 4. End of Season NDVI (EOSN): NDVI value at the ending time of the growing season (unitless-based on NDVI units) 5. Maximum Time (MAXT): the day of the year when the NDVI reaches its maximum during the growing season (in day of the year). 6. Maximum NDVI (MAXN): the highest (or peak) value in NDVI observed in a growing season (unitless-based on NDVI units). 7. Duration (DUR): the length of the growing season-the time between the start of season and end of season (in number of days). 8. Amplitude (AMP): the difference between the Maximum NDVI and NDVI at the day of start of season (unitless-based on NDVI units). 9. Time Integrated NDVI (TIN): the cumulative value of NDVI from the start to the end of the growing season (unitless-based on accumulated NDVI units).